The number that matters most with spider veins is not how many veins disappear on the first visit. It is how much improvement the sources say to expect and what that leaves you to plan for. This article walks through it for a reader in Ann Arbor, Michigan.
The two common options
Harvard Health names them: "The two most common cosmetic treatments for spider veins are laser treatment and sclerotherapy: Laser treatment directs pulses from a laser light to the spider veins, causing tiny blood clots to form." Its page on spider veins is the source for both the options and the figure below.
What improvement means in practice
The same page sets the expectation: "If you decide on cosmetic treatment for your spider veins, you can expect a 50% to 90% improvement." That is a wide range, and it describes improvement, not clearance. The gap between the low end and the high end is the part to ask a practice about.
Follow-up and upkeep
Improvement at either end of that range can still leave visible veins, so ask whether a second round is part of the plan. The page at aad.org explains why leg veins appear and how dermatologists treat them, which helps you judge a practice's plan against a dermatology reference.
What to ask before you commit
Ask which of the two options the practice would use for your veins, where in the 50% to 90% range it expects you to land, and what a second round would cost.